Macromolecules Volume 27, Number 18
August 29, 1994
0 Copyright 1994 by the American Chemical Society
Synthesis of 7,7,8-Tris(alkoxycarbonyl)-8-cyanoquinodimethanes and Their Amphoteric Polymerization Behavior in Alternating Copolymerization Takahito Itoh,' Nobuaki Kamei, and Shouji Iwatsuki' Department of Chemistry for Materiak, Faculty of Engineering, Mie University, Kamihama-cho, Tsu 514, Japan Received March 7, 1994; Revised Manuscript Received May 26,1994* ABSTRACT 7,7,8-Tris(alkoxycarbonyl)-8-cyanoquinodimethanes(1) with ethoxy (la), methoxy (lb), isopropoxy (IC), butoxy (Id),and tert-butoxy (le)alkoxy groups were successfully prepared as pure, isolable yellow crystals. Compounds la and le formed charge-transfercomplexes not only with styrene (St) but also with 7,7,8,8-tetracyanoquinodimethane(TCNQ), indicating that la and le exhibited an amphoteric polar character in the charge-transfercomplex formation. When la-e were dissolved in basic polar aproticsolvente such as acetone, acetonitrile, tetrahydrofuran,NJV-dimethylformamide, and dimethyl sulfoxide, la-d, but not le,spontaneously polymerized to give polymers. Compounds la-e were homopolymerizable with 2,2'azobis(isobutyronitri1e)(AIBN)and butyllithium but not with boron trifluoride etherate. Compound le had a very poor polymerizability compared with la-d, probably due to the steric hindrance of the tert-butyl group. Homopolymerizable compound la copolymerized with St in the presence of AIBN to obtain the monomer reactivity ratios rl. = 1.62 f 0.28 and rst = 0.005 f 0.01 at 60 "C and Q and e values of Q = 30.5 and e = +1.40, indicating that la is highly conjugative (highly reactive) and electron-accepting and copolymerized with acceptor monomer TCNQ in a perfectly alternatingfashion. Poorly homopolymerizable compound le also copolymerized not only with donor monomer St but also with acceptor monomer TCNQ in a perfectly alternating fashion, indicative of the amphoteric polymerization behavior of le. Compounds la and le were found to be isolable lP-quinodimethanemonomers which exhibited amphoteric behavior in the charge-transfer complex formation as well as in the alternating copolymerization.
Introduction Unsubstituted 1,Cquinodimethane (QM) is so reactive that it gives polymeric materials immediately at room temperature.l Introduction of electron-withdrawing substituents such as cyano and ester groups on its exocyclic carbon makes QM less reactive, and crystalline materials may be obtained at room temperature: e.g., 7,7,8,8tetracyanoquinodimethane (TCNQ),2 7,7,8,8-tetrakis(methoxycarbony1)quinodimethane (TMCQ),2 7,7,8,8tetrakis(ethoxycarbony1)quinodimethane (TECQ),3 7,8bis(alkoxycarbonyl)-7,&dicyanoquinodimethanes (ACQ),a5 and so on. These isolable, electron-accepting quinodimethanes show different polymerization behaviors depending on the nature and number of the electronwithdrawing substituents. TCNQ carrying four cyano groups at the 7 and 8 positions is not homopolymerizable with any initiator but is copolymerizable as an acceptor monomer with a donor monomer such as styrene (St) in an alternating fashion.6 TMCQ carrying four ester groups
* Abstract published in Advance ACS Abstracts, July 15, 1994.
is homopolymerizable, but TECQ is not homopolymeri ~ a b l e .Their ~ ~ ~polymerizability depends on the nature of the alkoxy groups. Moreover, both TMCQ and TECQ copolymerized alternatingly in an amphoteric that is, they can copolymerize not only as acceptor monomers toward the donor monomer St but also as donor monomers toward the powerful electron-accepting monomer TCNQ. ACQ carrying two different electronwithdrawing substituents such as cyano and ester groups is homopolymerizable with radical and anionic initiators and copolymerizable with St in a random fashion.598 As the polymerization behavior of the electron-accepting 1,4quinodimethanes greatly depends on their substitution mode, we are interested in the polymerization behavior of a new type of isolable 1,6quinodimethanes with substitution mode different from the 1,Cquinodimethanes mentioned above. In this work are described the syntheses and polymerizations of 7,7,8-tris(alkoxycarbonyl)-8-cyanoquinodimethanes (la-) with ethoxy, methoxy, isopropoxy, butoxy, and tert-butoxy alkoxy groups, respectively, as a
0024-9297/94/2227-4859$04.50/00 1994 American Chemical Society
Macromolecules, Vol. 27, No. 18, 1994
4860 Itoh e t al. new type of isolable, electron-accepting 1,4-quinodimethanes. ROOC
COOR
a: CYCH, b: CH, NC'COOR
c : CH(CH,), d: CYCH,CYC& e : C(CH,h
I
Experimental Section Preparation of 7,7,8-Tris(alkoxycarbonyl)-8-cyanoquinodimethane (1). The preparations of 8-[cyano(ethoxycarbonyl)methylene]-1,4-dioxaspiro[4.5]decane (3a), 8-[cyano(methoxycarbonyl)methylene]-1,4-dioxaspiro[4.5]decane (3b), 8- [cyano(isopropoxycarbonyl)methylene]-1,Cdioxaspiro [4.5]decane (3c),8-[cyano(butoxycarbonyl)methylene]- 1,4dioxaspiror4.51decane (3d),4- [cyano(ethoxycarbonyl)methylene]cyclohexanone (4a),4-[cyano(methoxycarbonyl)methylene]cyclohexanone (4b), 4[cyano(isopropoxycarbonyl)methylene] cyclohexanone (4c), and 4-[cyano(butoxycarbony1)methylene]cyclohexanone (4d) were described in a related paper? 8-[Cyano( tert-butoxycarbonyl)methylene]-1,4-dioxaspiro[4.51decane (38). 1,4-Cyclohexanedionemonoethylene ketal (2) (10.0 g, 64.0 mmol) and 9.05 g (64.1 mmol) of tert-butyl cyanoacetate were refluxed in the presence of 1.0 g of ammonium acetate and 3.0 g of acetic acid in 20 mL of benzene using a Dean-Stark water separator to isolate water formed for 1h. The reaction mixture was washed with 20 mL of saturated sodium chloride aqueous solution and 20 mL of saturated sodium bicarbonate aqueous solution and dried over anhydrous magnesium sulfate. It was placed under reduced pressure to remove solvent to obtain a white solid, which was recrystallized from hexane to give 13.0 g (74% yield) of 3e as white plates: mp 75.076.0 "C; IR (KBr) UCH 2940, UCN 2204, v~ 1685, vc-c 1571, vm 1239,1076 cm-I; lH NMR (CDCl3) 6 3.99 (s,4H), 3.13 (t, J = 7.0 Hz, 2H), 2.82 (t, J = 7.0 Hz, 2H), 1.87 (t,J = 7.0 Hz, 2H), 1.82 (t, J = 7.0 Hz, 2H), 1.53 (8, 9H). Anal. Calcd for C~E&NO~: C, 65.44; H, 6.22; N, 5.09. Found: C, 65.21; H, 6.31; N, 4.91. 4-[Cyano( t e r t - b u t o x y c a r b o n y 1 ) m e t h y l e n e l c y c l o hexanone (4e). Ketal 38 (13.0 g, 47.1 mmol) was added to 270 mL of tetrahydrofuran containing 30 mL of 20% hydrochloric acid and then stirred a t room temperature for 40 h. The reaction mixture was placed under reduced pressure to remove tetrahydrofuran and then extracted with 200 mL of ethyl acetate. The extract was washed with 100 mL of saturated sodium chloride aqueous solution and 100 mL of saturated sodium bicarbonate aqueous solution, dried over anhydrous magnesium sulfate, and then placed under reduced pressure to remove solvent to give a white solid, which was recrystallized from hexane to obtain 10.41 g (96% yield) of 46 as white plates: mp 78.0-80 "C; IR (KBr) YCH 2940, UCN 2208, v+.o 1683, U C 1573, ~ v1243, 1079 cm-'; 'H NMR (CDC13) S 3.37 (t,J = 6.9 Hz, 2H), 3.10 (t, J = 6.9 Hz, 2H), 2.56 (t, J = 6.9 Hz, 2H), 2.54 (t, J = 6.9 Hz, 2H), 1.55 (s, 9H). Anal. Calcd for C13HlsNOs: C, 67.52; H, 5.67; N, 6.06. Found: C, 67.41; H, 5.31; N, 5.89. l-[Cyano(ethoxycarbonyl)methylene]-4-[bis(ethoxycarbonyl)methylene]cyclohexane (5a). Titanium tetrachloride (8 mL, 72.8 mmol) in 16 mL of carbon tetrachloride was added to 100 mL of tetrahydrofuran a t 0 OC, and then into the yellow suspension was added 5.80 g (31.0 mmol) of 4-[cyano(ethoxycarbonyl)methylene]cyclohexanone(4a)and 4.96 g (31.0 mmol) of diethyl malonate. To the resulting brown suspension was added 12mL (149mmol) of pyridine in 13mL of tetrahydrofuran over a period of about 30 min, and the mixture was stirred at room temperature for 3 days. The reaction mixture was poured into 200 mL of water and then extracted three times with 50 mL of ethyl acetate. The extracts were combined,successivelywashed with 50 mL of saturated sodium chloride aqueous solution, 50 mL of saturated sodium bicarbonate aqueous solution, and 50 mL of saturated sodium chloride aqueous solution, dried over anhydrous magnesiumsulfate, and placed under reduced pressure to remove solvent to give a pale brown viscous oil, which was
dissolved in a small amount of isopropyl ether. The resulting solution was passed through a silica gel column using isopropyl ether as an eluent. The second elution band was collected and placed under reduced pressure to remove solvent to leave a white solid, which was recrystallized twice from hexane to give 7.36 g (68% yield) of 5a as white needles: mp 63.5-64.5 "C; IR (KBr) YCH 2944, V C N 2202, v w 1670, -v 1570, YGO 1224, 1093 cm-l; lH NMR (CDC13) 6 4.26 (m, 6H), 3.17 (t, J = 6.2 Hz, 2H), 2.87 (s,4H), 2.76 (t,J = 6.2 Hz, 2H), 1.31 (m, 9H). Anal. Calcd for ClsHz3NOs: C, 61.88; H, 6.64; N, 4.01. Found: C, 61.83; H, 6.42; N, 3.91. 1-[Cyano(methoxycarbonyl)met hylene]-4-[ bis(methoxycarbonyl)methylene]cyclohexane (5b). Compound 5b was obtained as white needles in 60% yield from the reaction of 4- [cyano(methoxycarbonyl)methylenelcyclohexanone(4b) with dimethyl malonate in a process similar to that for 5a: mp 103.7104.3 "C; IR (KBr) YCH 2920, Y C N 2202, vc=o 1684, vc=.6 1568, v w 1229,1092cm-l; lH NMR (CDC13) 6 3.81 (s,3H),3.77 (s,6H),3.18 (t, J = 6.3 Hz, 2H), 2.87 (s,4H), 2.74 (t,J = 6.3 Hz, 2H). Anal. Calcd for C16H17NOs:C, 58.63;H, 5.58; N, 4.56. Found: C, 58.39; H, 5.71; N, 4.61. 1-[Cyano(isopropoxycarbonyl)methylene]-4-[ bis(isopr0poxycarbonyl)methylene]cyclohexane (5c). Compound 5c was obtained as white needles in 65 % yield from the reaction of 4-[cyano(isopropoxycarbonyl)methylenelcyclohexanone (4c)with diisopropyl malonate in a process similar to that for 5a: mp 52.0-52.5 "C; IR (KBr) YCH 2944, YCN 2202, vcp.0 1671, v c d : 1570, u r n 1230, 1091 cm-l; lH NMR (CDC13) 6 5.15 (m, 3H), 3.18 (t, J = 6.6 Hz, 2H), 2.86 (s, 4H), 2.75 (t, J = 6.6 Hz, 2H), 1.34 (d, J = 6.3 Hz, 6H), 1.28 (d, J = 6.3 Hz, 12H). Anal. Calcd for C21HHN06:C, 64.43; H, 7.47; N, 3.58. Found: C, 64.51; H, 7.18; N, 3.69. l-[Cyano(butoxycarbonyl)methylene]-4-[bis( butoxycarbonyl)methylene]cyclohexane (5d). Compound 5d was obtained as white needles in 66% yield from the reaction of 4-[cyano(butoxycarbonyl)methylenelcyclohexanone (4d) with dibutyl malonate in a process similar to that for 5a: mp 41.C42.0 "C; IR (KBr) Y C H 2920, VCN 2202, -v 1688, vc-c 1571, v w 1223, 1094 cm-l; lH NMR (CDCl3) 6 4.20 (m, 6H), 3.18 (t, J = 6.2 Hz, 2H), 2.87 (s, 4H), 2.76 (t, J = 6.6 Hz, 2H), 1.64 (m, 6H), 1.38(m, 6H),0.93 (m, 9H). Anal. Calcdfor CuI&NOs: C, 66.49; H, 8.14; N, 3.23. Found: C, 66.51; H, 8.18; N, 3.41. 1-[Cyano(tert-butoxycarbonyl)methylene]-4-[bis(tertbutoxycarbonyl)methylene]cyclohexane (5e). Compound5e was obtained as white needles in 63 76 yield from the reaction of 4-[cyano(tert-butoxycarbonyl)methylene]cyclohexanone (4e)with di-tert-butyl malonate in a process similar to that for 5a: mp 112-113 "C: IR (KBr) YCH 2942, UCN 2202, -v 1684, v~ 1571, V1236,1091 cm-1; lH NMR (CDCl3) 6 3.14 (t, J = 6.3 Hz, 2H), 2.83 (s, 4H), 2.72 (t, J = 6.3 Hz, 2H), 1.52 (s,9H), 1.50 (s, 18H). Anal. Calcd for CzdH35NOs: C, 66.49; H, 8.14; N, 3.23. Found: C, 66.71; H, 8.23; N, 3.10. 7,7,8-Tris(ethoxycarbonyl)-8-cyanoquinodimethane (la). Compound 5a (2.0 g, 5.7 mmol) was dissolved in lo00 mL of benzene, and then into the resulting solution were added 16 g (186 mmol) of activated manganese dioxide and 10 g of 3A molecular sieves. The mixture was stirred at room temperature for 4 h and then filtered. The yellow filtrate was placed under reduced pressure to remove solvent to give a yellow solid which was dissolved in a small amount of dichloromethane. The resulting solution was passed through a silica gel column using dichloromethane as an eluent. The yellow elution band was collected and placed under reduced pressure to remove solvent to obtain a yellow solid, which was recrystallized from hexane to give 0.52 g (26% yield) of la as yellow needles: mp 120 "C (dec); IR (KBr) V C H 2946, YCN 2192, ve.0 1684, YC-C 1533, vc-0 1226, 1088 cm-1; 1H NMR (CDC13) 6 8.33 (dd, J = 2.0, 10.2 Hz, lH), 7.67 (dd, J = 2.0, 9.9 Hz, lH), 7.57 (dd, J = 2.0, 10.2 Hz, lH), 7.36 (dd, J = 2.0, 9.9 Hz, lH), 4.35 (q, J = 7.2 Hz, 4H), 4.34 (9, J=7.2Hz,2H),1.39(t,J=7.2Hz,6H),1.35(t,J=7.2Hz,3H); UV(CHC13)X 383 nm ( t = 4.16 X lo4). Anal. Calcd for ClgHlsNOs: C, 62.60; H, 5.55; N, 4.06. Found: C, 62.47; H, 5.29; N, 3.83. 7,7,8-Tris(methoxycarbonyl)-8-cyanoquinodimethnne (lb). Compound l b was obtained as yellow needles in 31 % yield from 5b in a process similar to that for la: mp 140 "C (dec);IR (KBr)
Macromolecules, Vol. 27, No. 18, 1994 YCH 2918, YCN 2200, u c - 0 1681, uc-c 1540, u w 1221, 1092 cm-l; 'H NMR (CDC13) 6 8.34 (dd, J = 2.0, 10.1 Hz, lH), 7.66 (dd, J = 2.0, 10.0 Hz, lH), 7.56 (dd, J = 2.0, 10.1 Hz, lH), 7.37 (dd, J = 2.0,lO.O Hz, lH), 3.91 (s,3H), 3.90 (8,6H); UV (CHC13) X 383 nm (e = 4.24 X 104). Anal. Calcd for C ~ ~ H I ~ NC,O59.41; ~ : H, 4.32; N, 4.02. Found: C, 59.21; H, 4.35; N, 3.88. 7 , 7 , 8 - T r i s ( isopropoxycarbonyl)-8-cyanoquinodimethane (IC). Compound ICwas obtained as yellow needles in 24% yield from 5c in a process similar to that for la: mp 77.5-78.0 "C; IR (KBr) VCH 2942, UCN 2188, u c - 0 1681, -V 1538, VU 1213, 1090 cm-l; lH NMR (CDCl3) 6 8.32 (dd, J = 2.0, 10.2 Hz, lH), 7.66 (dd, J = 2.0, 9.9 Hz, lH), 7.56 (dd, J = 2.0, 10.2 Hz, lH), 7.34 (dd, J = 2.0, 9.9 Hz, lH), 5.20 (m, 3H), 1.36 (d, J = 6.3 Hz, 6H), 1.33 (d, J = 6.3 Hz, 12H); UV(CHC13) X 384 nm (t = 3.95 X lo4). Anal. Calcd for CzlH25NO6: C, 65.10; H, 6.50; N, 3.62. Found: C, 65.31; H, 6.62; N, 3.81. 7,7,8-Tris(butoxycarbonyl)-8-cyanoquinodimethane (ld). Compound Id was obtained as yellow needles in 29% yield from 5d in a process similar to that for la: mp 72.5-73.0 "C; IR (KBr) VCH 2920, YCN 2183, u c - 0 1714, U C 1537, ~ UW 1224, 1094 cm-l; 'H NMR (CDCl3) 6 8.33 (dd, J = 2.0, 10.1 Hz, lH), 7.66 (dd, J = 2.0, 9.9 Hz, lH), 7.56 (dd, J = 2.0, 10.1 Hz, lH), 7.36 (dd, J = 2.0, 9.9 Hz, lH), 4.30 (t,J = 6.6 Hz, 4H), 4.29 (t,J = 6.6 Hz, 2H), 1.74 (m, 2H), 1.46 (m, 4H), 1.41 (m, 4H), 0.96 (t, J = 7.2 Hz, 2H), 0.95 (t, J = 7.3 Hz, 6H); UV (CHCla) X 384 nm (t = 4.08 X lo4). Anal. Calcd for CZ&NO~: C, 67.11; H, 7.28; N, 3.26. Found: C, 66.97; H, 7.12; N, 2.98. 7,7,8-Tris( tert-butoxycarbonyl)-8-cyanoquinodimethane (le). Compound l e was obtained as yellow needles in 26% yield from 5e in a process similar to that for la: mp 1678, u1535, 101-102 "C; IR (KBr) UCH 2940, VCN 2180, -V u r n 1227, 1090 cm-1; lH NMR (CDC13) 6 8.26 (dd, J = 2.0, 9.8 Hz, lH), 7.62 (dd, J = 2.0, 10.2 Hz, lH), 7.51 (dd, J = 2.0, 9.8 Hz, lH), 7.30 (dd, J = 2.0, 10.2 Hz, lH), 1.56 (s, 18H), 1.55 (s, 9H); UV (CHCls) X 384 nm (t = 4.36 X lo4). Anal. Calcd for C24H31N06:C, 67.11; H, 7.28; N, 3.26. Found: C, 67.28; H, 7.30; N, 3.24. UV-Vis Measurement for the la-St, la-TCNQ, le-St, and le-TCNQ Systems. Absorption spectra of the chargetransfer transition for four systems were taken in chloroform at room temperature. The concentrationsof the solutionsemployed were as follows: [la] = 4.93 x 103mol/L and [Stl = 0.37 mol/L for the la-St system, [la] = 5.55 X mol/L and [TCNQ] = 1.02 X 10-3 mol/L for the la-TCNQ system, [le] = 6.73 X 109 mol/L and [St] = 0.60 moliL for the lest system, and [le] = 4.22 X 10-2 mol/L and [TCNQ] = 9.84 X 10-4 mol/L for the leTCNQ system. Cyclic Voltammetry Measurement. Voltammetric measurement was carried out at room temperature at a scanning rate of 100 mV/s using dichloromethane as the solvent containing tetrabutylammonium perchlorate (0.1 mol/L) as the supporting electrolyte, and Ag/AgCl, glassy carbon, and platinum wire were used as the reference electrode, working electrode, and counter electrode, respectively. Spontaneous Polymerizations of la-e in Some Solvents. Compounds la-e (about 1mg) were dissolvedin 1mL of a solvent such as benzene, toluene, chloroform, acetone, acetonitrile, tetrahydrofuran, NJV-dimethylformamide, and dimethyl sulfoxide. After standing for 2 h at room temperature, an aliquot of the solution was taken out by a syringe and was subjected to gel permeation chromatography (GPC) to determine the molecular weight of the reaction product. Polymerization Procedure. Radical Polymerization. Givenamountsofla, lb, IC,ld,or le,StorTCNQasacomonomer if necessary, benzene or dichloromethane as a solvent, and 2,2'azobis(isobutyronitri1e)(AIBN) as a radical initiator were placed in a glass ampule, which was degassedby the freeze-thaw method (repeatedly three times) and sealed. The ampule was placed in a bath thermostated at 60 "C for the time of polymerization and then opened. The reaction mixture was poured into an excess of hexane to precipitate the product, which was purified in three or more redissolution-reprecipitation cycles. Dichloromethane and hexane were used as solvent and precipitant, respectively. When TCNQ was used as a comonomer, acetonitrile and methanol were used as solvent and precipitant, respectively. The product
Polymerization of Substituted Quinodimethanes
4861
obtained was dried under reduced pressure at room temperature until a constant weight was reached. Ionic Polymerization. The polymerization was carried out A given amount of la, with the apparatus reported previ~usly.~ lb, IC, Id, or le as a monomer was placed in the apparatus, which was filled with nitrogen. Into it was introduced a given amount of solvent by a syringe. After the resulting solution was degassed by the freeze-thaw method (repeated twice), the apparatus was filled with nitrogen and sealed. Then it was set in a bath thermostated at 0 "C, and a fixed amount of butyllithium, triethylamine, pyrrolidine, or boron trifluoride etherate was injected into it by a syringe. After a given time of the reaction, the reaction mixture was poured into excess hexane to deposit a polymeric product. The precipitated polymeric product was dissolved again in a small amount of dichloromethane, and the resulting solution was poured into hexane for purification. When no polymeric product was deposited in this process, the hexane solution was placed under reduced pressure to remove volatile materials. An aliquot of the residue was dissolved in a small amount of benzene, and the resulting benzene solution was subjected to GPC to determine the molecularweight of the reaction product. Other Materials. TECQ3 and 7,8-bis(ethoxycarbonyl)-7,8dicyanoquinodimethane (ECQ)4were prepared accordingto the methods reported previously. TCNQ was prepared accordingto the method reported by Acker et and recrystallized twice from acetonitrile. Styrene [bp 52 OC (30 mmHg)] was washed with 2% aqueous sodium hydroxide solution and water, dried over anhydrous magnesium sulfate, stirred over calcium hydride, and then distilled under reduced pressure. Chloroform (bp 61 "C), acetonitrile (bp 82 "C), dichloromethane (bp 40 "C), and acetone (bp 56 "C) were refluxed over calcium hydride for 12 h and then distilled. Tetrahydrofuran (bp 66 "C) was refluxed over lithium aluminum hydride for 12 h and then distilled. Dimethyl sulfoxide [bp 68 "C (10 mmHg)] and Nfl-dimethylformamide [bp 70 "C (10 mmHg)] were dried over 3A molecular sievesfor a day and then distilled under reduced pressure. AIBN was recrystallized from ethanol. Boron trifluoride etherate [bp 50 OC (50 mmHg)l was distilled under reduced pressure under nitrogen. Triethylamine (bp 89 "C) and pyrrolidine (bp 87 "C) were distilled over potassium hydroxide. Commercial tetrabutylammonium perchlorate, butyllithium, dimethyl malonate, diethyl malonate, dibutyl malonate, methyl cyanoacetate, ethyl cyanoacetate, isopropyl cyanoacetate, and butyl cyanoacetate were used without further purification. Di-tert-butyl malonate and diisopropyl malonate were prepared from the reactions of malonyl dichloride with tert-butyl alcohol and with isopropyl alcohol, respectively.1° tert-Butyl cyanoacetate was prepared according to the method reported by Ireland.ll Characterization. Copolymer composition was established by elemental analysis. Number-average molecular weights, M,,, of the homopolymersof la-e and the copolymersof la or le with St and of le and TCNQ were determined by GPC using standard polystyrenes as reference and tetrahydrofuran as an eluent without correction. Solution viscosity was determined at 30 OC in concentrated sulfuric acid for the copolymers of lawith TCNQ. 'H NMR measurement was carried out in chloroform-d with tetramethylsilane as an internal standard. The glass transition temperatures, Tgs, of the polymers were determined by differential scanning calorimetry (DSC) at a scanning rate of +10 OC/min under nitrogen. Instrumentation. A Buchi capillarymelting point apparatus was used for melting point measurement, a JEOL JNM-EX270 FT NMR spectrometer for 'H NMR spectroscopy,Jasco IR-700 and UVIDEC-430B spectrometers for infrared and UV-vis spectroscopy, respectively, a Yanaco CHN Corder MT-3 for elemental analysis, a GPC Tosoh HPLC-803D with a series of two columns (Tosoh G4000H and G3000H) for measuring number-average molecular weight (M"), and a Perkin-Elmer differential scanning calorimeter DSC-2C for thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC), respectively.
Results and Discussion Preparation. 7,7,8-Tris(alkoxycarbonyl)-8-cyanoquinodimethanes (la-e) with ethoxy, methoxy, isopropoxy,
4862 Itoh et al.
Macromolecules, Vol. 27,No. 18, 1994 Scheme 1
n Oxo
K
NCCHSWR
u-
I
0
x
0-0
Y -
H+
0.7
'I
'I
t
NC COOR
0 2
4.: Et 4b: Me
3.: Et
36:Me k:LPr
- Q
3c: bBo
ROOC,COOR
ROOC COOR
CH#XOR)P
NC
c:IPr 6:B" 6:t-Bu
3d: Bn
Q
MnO, ___f
OOR
NC
COOR
5.: Et
le: Et
5 b Me
Ib:
sc: LPr 5 d B" 5e: t.BO
le: IPr Id: Bu le: 1.6"
Me
Table 1. First Reduction Potentials of l,4-Quinodimethanes first reduction potential (V)a 1,4-quinodimethane
TCNQ ECQ
l b (Me) la (Et) Id (Bu) IC(iPr) le (tBu)
-
' \ _ \
0
' 40 0
+0.16 -0.12
-0.27
-0.32 -0.39 -0.40 -0.50 -0.86
TECQ Solvent, dichloromethane containing tetrabutylammonium perchlorate (0.1 mol/L); reference electrode, Ag/AgCl; scanning rate, 100 mV/s; relative error, iO.01 V.
butoxy, and tert-butoxy alkoxy groups were successfully prepared according to Scheme 1. 8-[Cyano(alkoxycarbonyl)methylenel-1,4-dioxaspiro[4.5ldecanes (3a-e) were prepared in good yield by the Knoevenagel reaction of 1,4-~yclohexanedionemonoethylene ketal (2) with alkylcyanoacetates in the presence of ammonium acetate and acetic acid in benzene for 3e and in the presence of @alanine in water for 3a-d. Ketal 3e was readily hydrolyzed with 20 % hydrochloric acid in tetrahydrofuran at room temperature and ketals 3a-d with 2% sulfuric acid aqueous solution to give 4-[cyano(alkoxycarbonyl)methylenelcyclohexanones (4a-e) in quantitative yields. 4-[Cyano(alkoxycarbonyl)methylene]cyclohexanones (4a-e) were subjected to the Knoevenagel reaction with alkyl malonates using titanium tetrachloride and pyridine as the dehydrating system to give 1-[cyano(alkoxycarbony1)methylene]-4-[bis(alkoxycarbony1)methylenelcyclohexanones (5a-e) in moderate yields, which were readily oxidized with activated manganese dioxide in the presence of 3A molecular sieves in benzene to give 7,7,8-tris(alkoxycarbonyl)-8-cyanoquinodimethanes (la-e) as yellow needles. Their IR and 'H NMR spectra and elemental analyses strongly supported the chemical structures of 7,7,8,8-tetrasubstituted1,4quinodimethanes. The total yield in four steps was 1015%. Electron-Accepting Character. The electronaccepting character of la-e was estimated as the value of the first reduction potential, E l , by cyclic voltammetry. The values for la-e are summarized in Table 1,together with those of TCNQ, ECQ, and TECQ for comparison. It is obvious that la-e are weaker in electron-accepting character than TCNQ and ECQ and stronger in electronaccepting character than TECQ as expected from the difference in the electron-accepting character between the cyano and ester groups and the number of them. Moreover, the electron-accepting character of la-e can be explained fairly well in terms of Taft's polar substituent constant
\
500
I
600
Wavelength, nm
Figure 1. UV-vis spectra of a mixture of le with St in chloroform: (-) spectrum of a mixture of le with St; (--) spectrum of le; (.) difference spectrum between the above two spectra, corresponding to that of the complex. (--) Difference spectrum between la and a mixture of la and St. (--) Difference spectrum between TECQ and a mixture of TECQ with St. Concentrations of solutions employed are [la] = 4.94 x 103 mol/L and [St] = 0.37 moVL for the la-St system, [le] = 6.73 X 103 mol/L and [St] = 0.6 mol/L for the le-St system, and [TECQ]= 1.02 X Wmol/L and [St]= 0.94 moVL for the TECQSt system. I
I
/
I
Wavelength, nm
Figure 2. UV-vis spectra of a mixture of le with TCNQ in chloroform: (-) spectrum of a mixture of le with TCNQ; (- -) spectrum of le; (-3spectrumof TCNQ; differencespectrum, corresponding to that of the complex. (--) Difference spectrum between la and a mixture of la and TCNQ. Concentrationsof solutions employed are [la] = 5.55 X 10-*mol/L and [TCNQ] = 1.02 X 103 mol/L for the la-TCNQ system and [le] = 4.22 x le2mol/L and [TCNQ] = 9.84 X lo-' mol/L for the le-St (-a)
system.
values,12up*, of the methyl (O.O), ethyl (-0.100), isopropyl (-0.190), butyl (-0.130),and tert-butyl (-0.300) groups. Charge-Transfer Absorption Band. Addition of St to le in benzene caused the yellow color of the le solution to deepen as shown in Figure 1, where the difference spectrum between the mixture and le shows a broad absorption band in the wavelength range 460-580 nm, corresponding to the charge-transfer transition between le and St. St does not absorb any light at wavelengths
Macromolecules, Vol. 27, No. 18, 1994
Polymerization of Substituted Quinodimethanes 4863
Table 2. Spontaneous Polymerizations of la-e in Various Aprotic Polar Solvents
ofMeOW 49 acetonitrile 62 acetone tetrahydrofuran 93 Nfl-dimethylformamide 107 dimethyl sulfoxide 141
la 15 20 0.75 20 100
lb lo 3 4.5 3.5 4.5 1.8 4 2 5 4.5 5
Id le 3.5 3 2 4 4 -
a As solvent basicity, the v(OD) stretching frequency shift of methanol-d due to hydrogen bond formation with the solvent was determined.
longer than 400 nm. The corresponding absorption band between TECQ and St exists in the wavelength range 440500 nm as shown in Figure 1. From comparison of both absorption bands, it may be said that le is a stronger electron acceptor than TECQ, corresponding well with the results obtained by cyclic voltammetry: le (El = -0.50 V) and TECQ (E1 = -0.86 V). The charge-transfer transition spectrum between le and TCNQ is shown in Figure 2, where the difference spectrum between the mixture and the components reveals a broad absorption band in the wavelength range 520-580 nm though the absorbance is weak. It seems that le interacts as a donor compound with TCNQ, indicating that there exists a sufficient difference in electron density for the chargetransfer complexation between le and TCNQ. When la was used instead of le, the charge-transfer transition spectra between la and St and between la and TCNQ exhibit broad absorption bands in the wavelength ranges 460-580 nm in Figure 1 and 500-590 nm in Figure 2, respectively. Consequently, it can be pointed out that la and le exhibit amphoteric polar character in their chargetransfer complex formation as well as TMCQ" and TECQS3 Homopolymerizations. The polymerization behavior of la-e dissolved in various solvents was examined. In so-called nonpolar common solvents such as toluene, benzene, chloroform,and dichloromethane, all compounds remained yellow for 24 h, and their GPC chromatograms showed only peaks as the monomer state. In so-called
basic aprotic polar solvents such as dimethyl sulfoxide, N,N-dimethylformamide, tetrahydrofuran, acetone, and acetonitrile, la-d, but not le, changed in a few minutes from yellow to colorless in dimethyl sulfoxide, N,Ndimethylformamide, acetone, and acetonitrile and changed slowly in 24h from yellow to pale yellow in tetrahydrofuran. After standing for 2 h, compounds la-d in such basic aprotic polar solvents were subjected to GPC, the chromatograms of which exhibited two peaks, one for la-d themselves and the other for polymers of la-d with molecular weights of 0.75 X lo3 to 1.0 X lo6 as shown in Table 2. However, le in such basic aprotic solvents remained yellow for 24 h, and its chromatograms showed only a peak for le itself, indicating that le is not homopolymerizable in those solvents. It was found that la-d, but not le, are spontaneously polymerizable with basic aprotic polar solvents as well as ECQ,4 7,8-bis(butoxycarbonyl)-7,&dicyanoquinodimethane (BCQ),6 7,& diacyl-7,8-dicyanoquinodimethane(AcCQ),13 and 7,8dibenzoyl-7,8-dicyanoquinodimethane( B z C Q ) . ~ ~ Homopolymerizations of la-e were carried out with the radical initiator AIBN, the anionic initiator butyllithium, and the cationic initiator boron trifluoride etherate. Homopolymerizations of la were also carried out with the weak bases triethylamine and pyrrolidine. The polymerization results are summarized in Table 3. Polymers were obtained as white powders, which were soluble in chloroform, dichloromethane, tetrahydrofuran, acetone, and ethyl acetate and insoluble in hexane and methanol. It can be pointed out from Table 3 that la-e are homopolymerizable with the radical and anionic initiators but not with the cationic initiator. For the polymerizations of la-e under the conditions with monomer concentration of 0.16 mol/L in the presence of AIBN at 60 "C for 24 h, the polymer yield for le is much lower than those for lad, indicating that the polymerizability of le is much less than those of la-d. Previously, it was pointed out that the polymerizability of 7,8-diacyl-7,8-dicyanoquinodimethanes greatly depends on the steric effect of the acyl groups.14 Taft's steric substituent constants,12E,, of the methyl, ethyl, isopropyl, butyl, and tert-butyl groups as
Table 3. Homopolymerizations of la-e solvent [la-e] (mol/L) temp ("C) l a (R = Et) 60 benzene 0.16 60 1 56.4 AIBN 2 52.1 BFs.Eh0 10 CHCls 0.03 0 3 55.5 BuLi 10 toluene 0.03 0 4 54.7 EtsN 10 toluene 0.03 0 5 66.8 EtsN 0.1 toluene 0.03 0 6 65.6 pyrrolidine 10 toluene 0.03 0 7 54.0 pyrrolidine 0.1 toluene 0.03 0 l b (R = Me) 8 54.9 AIBN 60 benzene 0.16 60 9 50.8 BFrEh0 10 CHCls 0.03 0 10 51.3 BuLi 10 toluene 0.03 0 IC (R = iPr) 11 50.6 AIBN 60 benzene 0.16 60 12 52.3 BFrEh0 10 CHCls 0.03 0 13 49.0 BuLi 10 toluene 0.03 0 Id (R = Bu) 14 50.9 AIBN 60 benzene 0.16 60 15 54.3 BFrEh0 10 CHC13 0.03 0 16 55.6 BuLi 10 toluene 0.03 0 le (R = tBu) 17 62.0 AIBN 60 benzene 0.16 60 18 54.9 BFpEtzO 10 CHC13 0.03 0 19 58.2 BuLi 10 toluene 0.03 0 a Determined by GPC using tetrahydrofuran as an eluent and standard polystyrenes as reference.
run no.
la-e (mg)
initiator
[la-el/[initiatorl
time (h)
conv (%)
MJ10"a
24 6 6 6 0.25 6 0.5
86.3 0 19.6 48.1 100 15.0 93.0
5.9 2.0 10.0 4.0 0.23
-
24 6 6
92.0 0 12.4
0.4
24 6 6
81.5 0 10.5
9.0
24 6 6
91.0 0 8.0
9.5
24 6 6
3.2 0 5.4
2.5
1.8
2.5
1.3
0.2
Itoh et al.
4864
Macromolecules, Vol. 27, No. 18, 1994 C
J
1 0 1
I
9
8
200
400 Temperature ,OC
I
7
6
5
6
6
3
2
1
0
b) DSC
#PPm
$1
Figure 3. 1H NMR spectrum of the reaction product of le with pyrrolidine obtained under the condition of [le]/[pyrrolidinel = 0.1.
w
alkyl groups on the alkoxycarbonyl of 1are reported to be 0.0, -0.07, -0.47, -0.39, and -1.54, respectively, indicating that the E, value of tert-butyl group is much larger than those of the other groups. Therefore, it is considered that the poor polymerizability of le is probably attributable to the bulkiness of the tert-butyl group. Here, as the ethyl group is larger in steric hindrance than the methyl group, l a is expected to be less reactive on polymerization than lb. However, it was found from Table 3 that la is more reactive on polymerization than lb. Therefore, it is likely that factors other than steric hindrance also affect the polymerizability, though the factors are not clear at present. The polymerization of la with weak bases such as triethylamine and pyrrolidine under the condition of [la]/ [base] = 10 gave polymers with molecular weights of 1 X lo5and of 2.3 X lo3,respectively. Under the condition of [la]/[basel = 0.1, the polymerization of la with triethylamine gave a polymer with a molecular weight of 4 X lo4, but that with pyrrolidine gave no polymer, though the system changed from yellow to colorless instantaneously. So, the reaction mixture with pyrrolidine was placed under reduced pressure to remove solvent, and the residue was treated with chromatography using a silica gel column and chloroform as an eluent to give 61 mg (93% yield based on la) of a colorless viscous oil. Its IR spectrum showed absorption bands at 2232 cm-l due to the cyano group and at 1694 and 1226 cm-l due to the ester group. Its lH NMR spectrum in chloroform-d is shown in Figure 3, where individual peaks are assignable to the respective individual protons of the chemical structure illustrated therein. The elemental analysis values (C, 63.51; H, 6.71; N,6.48) for the viscous oil were in good agreement with the calculated ones (C,63.45; H, 6.78; N, 6.73) of the chemical structure illustrated in the figure. It is obvious that the product is the 1:l adduct. Therefore, it is conceivable that an electron transfer reaction occurs between l a and pyrrolidine to give a zwitterion with pyrrolidinium ion and a-cyano-a-(ethoxycarbonyl)benzyl anion as terminals, as shown in Scheme 2, the anionic end of which is considered to be able to add a la monomer. When excess pyrrolidine is present, it is conceivable that a number of the zwitterions will be formed and an intermolecular proton transfer from a pyrrolidinium moiety to the anionic moiety will give the 1:1adduct before reaction with another la monomer. In the case of triet,hylamine. a similar reaction was considered to take
,
,
0
154 'C
,
100
,I 200
Tempera ture,'C
Figure 4. Thermal analysis of the polymer of la at an elevating rate of temperatureof 10 "C under nitrogen: (a)TGDTA curves; ( b ) DSC curve.
Scheme 2
la
Poly-la COOEt
place to form azwitterion with triethylammonium ion and a-cyano-a-(ethoxycarbony1)benzyl anion. However, since the quaternary ammonium ion has no hydrogen for the proton transfer reaction, it was thought that the zwitterion would be able to add a la monomer in preference to the termination reaction to give a polymer with a molecular weight of 4 X lo4. The polymer of la (run no. 1) is capable of being cast from chloroform solution to give a brittle film. The results of TG-DTA and DSC measurements for the polymer of la (run no. 1) are shown in parts a and b of Figure 4, respectively. Weight loss began at about 230 "C and the weight loss from 230 to 420 "C amounted to 55%,which approximately corresponds to the weight percent of the ethoxycarbonyl group to the la unit. The glass transition temperature, Tg,of the polymer of la was 154 "C as shown in Figure 4b. Copolymerizations. The copolymerizations of St with la and with le in the presence of AIBN were carried out in benzene at 60 "C with monomer concentrations of la of 0.15 mol/L and le of 0.12 mol/L. All copolymers were obtained as white powders, which were soluble in chloroform, dichloromethane, tetrahydrofuran, acetone, and ethyl acetate but insoluble in hexane and methanol. The results of the copolymerizations are summarized in Table
Polymerization of Substituted Quinodimethanes 4865
Macromolecules, Vol. 27, No. 18, 1994
run no.
9 10 11 12
13 14
Table 4. Copolymerizations. of St with la and with le in Benzene at 60 "C anal. monomer feed copolym compn l a or le (mg) St (mg) la or l e (mol % ) solv (mL) time (min) conv (%) % C % N la or l e (mol % I l a (R = Et) 2.5 1 17 9.0 50.0 589.1 69.51 3.11 49.8 4.7 8.5 1 17 50.0 303.9 68.41 3.26 55.3 9.8 68.55 3.24 54.6 50.0 201.3 1 17 7.0 8.4 13.3 2 17 67.41 3.40 99.9 196.0 60.9 9.8 64.1 199.8 113.5 34.7 4 15 66.89 3.47 249.8 54.7 6.8 57.9 5 15 65.25 3.70 75.5 5.3 64.1 6 15 299.7 50.7 64.95 3.73 77.8 6.6 85.7 64.02 3.86 399.7 39.9 75.2 8 15 le (R= tBu) 99.5 426.3 10.0 2 30 7.4 71.97 2.63 50.3 100.1 49.9 32.7 2 30 8.9 72.30 2.59 48.3 200.5 58.0 45.6 4 30 9.1 71.55 2.69 53.1 300.8 60.2 54.6 6 30 5.4 72.10 2.61 49.5 451.2 49.1 72.3 9 30 6.9 71.80 2.65 51.3 800.4 40.8 82.6 16 25 5.2 71.49 2.69 53.5
Md1O' 55 20 40 28 11
9 7 4 11
15 9 9 4 9
a [la] = 0.15 mol/L, [le] = 0.12 mol/L, and [AIBN] = 1.2 X 103 mol/L. Determined by GPC using tetrahydrofuran as an eluent and standard polystyrenes as reference.
Table 5. Copolymerizations. of TCNQ with l a and with le in Dichloromethane at 60 O C monomer feed la or le anal. copolym compn run no. la or l e (mg) St (mg) (mol % ) solv (mL) time (min) conv (7%) % C % N la or le (mol 7%) MJlO'b l a (R = Et) 1 60.4 349.5 9.3 3 10 4.2 65.49 12.51 51.1 2 80.3 111.2 29.8 4 10 5.8 65.56 12.72 50.1 3 120.8 35.3 66.9 6 10 7.1 65.64 12.95 49.1 4 401.6 25.2 90.4 20 10 8.2 65.31 12.31 52.0 le (R = tBu) 5 60.1 264.0 7.8 3 60 9.8 68.20 10.84 51.0 10 6 80.5 133.3 22.3 4 60 9.7 68.25 11.14 49.6 7 7 140.2 68.3 49.3 7 60 9.6 68.21 10.87 50.9 12 8 180.0 32.4 72.5 9 60 8.9 68.23 11.04 50.0 12 9 320.3 15.8 90.6 16 60 6.4 68.17 10.61 52.1 7
v,o (dL/g)c
0.76 1.23 0.67 0.57
[la] = 0.058 mol/L, [le] = 0.047 mol/L, and [AIBN] = 1.2 X 103mol/L. Determined by GPC using tetrahydrofuran as an eluent and standard polystyrenes as reference. Solvent, concentrated sulfuric acid; temperature, 30 "C; concentration, c = 0.04-0.1 g/dL.
0 0
50
100
1 mol"/. in monomer feed
Figure 5. Copolymerization composition curves for the copolyand with le ( 0 )in benzene at 60 merization of St with la (0) "C.
4, and the copolymerization composition curves are shown
in Figure 5. The results for the la-St system were rationally analyzed according to the intersectionl5 and Kelen-Tudos16 methods to obtain monomer reactivity ratios rla = 1.62 f 0.28 and rst = 0.005 f 0.01 at 60 OC. The Alfrey-Price Q and e values of la were calculated on the basis of the monomer reactivity ratios to be 30.5 and +1.40,respectively, indicating that la is highly conjugative (highly reactive) and electron-accepting similar to BCQ,5 AcCQ,13andBzCQ.13The copolymersfor the le-St system were always composed of about 50% of the le unit regardless of the monomer feed ratios, indicating that le is copolymerizable with St in a perfectly alternating fashion. It is obvious that la and le react as acceptor monomers toward St. The difference in the copolymer-
ization fashions between la and le probably corresponds to the difference in homopolymerizability of homopolymerizable compound la and poorly homopolymerizable compound le, and it can be explained in terms of our mechanism of alternating copolymerization in connection with equilibrium polymerization behavior.17 The copolymerizations of TCNQ with la and with le in the presence of AIBN were carried out in dichloromethane at 60 "C with monomer concentrations of la of 0.058 mol/L and le of 0.047 mol/L. All copolymers were obtained as white powders. The copolymers for the la-TCNQ system are only soluble in hot concentrated sulfuric acid and insoluble in common organic solvents, and those for the le-TCNQ system are soluble in chloroform, dichloromethane, tetrahydrofuran, acetone, and ethyl acetate and insoluble in hexane and methanol. The results of both copolymerizations are summarized in Table 5, and the copolymerization composition curves are shown in Figure 6. The copolymerizations of TCNQ with la and with le were found to take place in a perfectly alternating fashion, indicating that both la and le react as donor monomers toward TCNQ. It is concluded, therefore, that when compounds 1 are poorly homopolymerizable or nonhomopolymerizable as is le, compounds 1 can amphoterically copolymerize as can TMCQ7 and TECQ.3 In summary, 7,7,8-tris(alkoxycarbonyl)-8-cyanoquinodimethanes (la-e) with methoxy, ethoxy, isopropoxy, butoxy, and tert-butoxy alkoxy groups were successfully prepared as pure, isolable yellow crystals. Compounds la and le exhibited an amphoteric polar character in charge-
4866 Itoh et al.
Macromolecules, Vol. 27, No. 18, 1994
100
zation behavior in their alternating copolymerizations. It was found that la and le are another type of isolable 1,4-quinodimethane monomer showing amphoteric behavior in charge-transfer complex formation as well as in the alternating copolymerization,though they are stronger in electron-accepting character than both TMCQ and TECQ.
10
50
100
1 mol% in monomer feed
Figure 6. Copolymerization composition curves for the copolymerization of TCNQ with la (0) and with le ( 0 )in dichloromethane a t 60 OC.
transfer complex formation. When la-e were dissolved in basic polar aprotic solvents such as acetone, acetonitrile, tetrahydrofuran, Nfl-dimethylformamide, and dimethyl sulfoxide, la-d, but not le, spontaneously polymerized to give polymers. Compounds la-e were homopolymerizable with radical and anionic initiators but not with a cationic initiator. It was found that le is less reactive on polymerization than la-d, probably due to the bulkiness of the tert-butyl group. Compound la was copolymerizable in the presence of AIBN to obtain the monomer reactivity ratios ria = 1.62 f 0.28 and rst = 0.005 f 0.01 at 60 "C and Q and e values of Q = 30.5 and e = +1.40,indicating that la was highly conjugative (highly reactive) and electronaccepting and copolymerized with acceptor monomer TCNQ in a perfectly alternating fashion. Poorly homopolymerizable compound le copolymerized not only with St but also with TCNQ in a perfectly alternating fashion. Compounds la and le exhibited amphoteric polymeri-
References and Notes (1) Errede, L. A.;Gregorian, R. S.; Hoyt, J. M. J. Am. Chem. SOC. 1960,82,5218. (2)Acker, D. S.;Hertler, W. R. J. Am. Chem. SOC. 1962,84,3370. (3) Iwatsuki, S.; Itoh, T.; Yokotani, I. Macromolecules 1983,16, 1817. (4) Iwatsuki, S.;Itoh, T.; Niehihara, K.; Furuhashi, H. Chem. Lett. 1982,517. (5) Iwatsuki, S.;Itoh,T.; Iwai,T.; Sawada,H. Macromolecules1985, 18,2726. (6) Iwatsuki, S.;Itoh, T.; Horiuchi, K. Macromolecules 1978,11, 491. (7)Iwatsuki, S.;Itoh, T. Macromolecules 1980,13, 983. (8) . . Iwatsuki. S.: Itoh.T.:Hieuchi. T.: Enomoto. K.Macromolecules 1988,21,' 1571. (9) Iwatsuki, S.;Itoh, T.; Meng, X . 4 . Macromolecules 1993,26, .
I
1910
ILLr).
(10) Raha, C. Organic Synthesis; Rabiohn, N., Ed.; Wiley: New York, 1963;Collect. Vol. 4,p 263. (11) Ireland, R. E.; Chaykovsky, M. OrganicSynthesis; Baumgarten, E. M., Ed.; Wilev: New York, 1973;Collect. Vol. 5,D 171. (12) Taft, R. W., Jr.-Separation of Pol& Steric, and Resonance
Effects in Reactivity. In Steric Effects in Organic Chemistry; Newman, M. S., Ed.; Maruzen: Tokyo, 1956;p 556. (13) Iwatsuki, S.;Itoh, T.; Sato, T.; Higuchi, T. Macromolecules 1987,20,2651. (14)Iwatsuki,S.;Itoh, T.;Yabunouchi,H.; Kubo, M.Macromolecules 1990,23,3450. 1944,66,1594. (15) Mayo, F. R.; Lewis, F. M. J. Am. Chem. SOC. (16) Kelen, T.;TtidBs, F. J. Macromol. Sci., Chem. 1979,A9, 1. (17)Iwatsuki, S.;Itoh, T.;Higuchi,T.;Enomoto, K. Macromolecules 1988,21, 1571.
